Various methods have been employed for extracting lipids from biomass. Techniques include direct extraction of the biomass with solvents, heating, pressure waves generated via electric arcs, direct saponification via KOH and ethanol, sonication, freezing and grinding and bead mills. For example, the biomass can be dried and the lipid extracted with a solvent such as hexane. Alternatively, a microbial fermentation broth can be subjected to extreme conditions of pH and/or temperature or additional equipment such as a homogenizer or pressure disruption device can be used to disrupt the cells. Some microbial biomasses such as Crypthecodinium cohnii have proven to be especially difficult to extract. Current methods to disrupt Crypthecodinium biomass include methods such as the one described in Triplett et al., Molecular Marine Biology and Biotechnology 2:239-245 (1993). Triplett uses glass beads to disrupt Crypthecodinium cells. Other methods include pressure disruption of a hexane-treated spray dried biomass, using high pressure drops of 12,000 to 20,000 psi to achieve satisfactory breakage of the cells.
Problems with prior methods include poor product quality due to chemically aggressive conditions of high temperature and high pH, high costs due to the need to spray dry the biomass or for additional equipment such as homogenizers and pressure vessels. Spray drying contributes considerably due to costs and the time required to spray dry. Furthermore, eliminating spray drying is advantageous because spray drying exposes the biomass to the high temperatures that are characteristic of a spray dryer. High temperatures may cause undesirable degradation and oxidation of the lipids. Use of prior methods of high pressure disruption necessitates frequent downtime to allow for maintenance of the cell breakage equipment. Even short periods of downtime are costly to the overall process.
The oxidative state of the lipid or lipid-containing material is strongly impacted by the processing conditions used to make the material. For food materials, the conditions during processing as well as the actual ingredients and quality of the ingredients will affect the oxidation state. For fermentation-derived lipids (e.g., lipids obtained from microbes grown in fermentors, ponds, etc.), the ingredients (fermentation and post-fermentation) used as well as the conditions during the lipid extraction and fermentation will affect the quality. Other sources of PUFAs, such as agricultural crops and animal sources, will also be affected by the processing conditions used to obtain the lipids and lipid-containing materials.